THE ACID OPEN-HEARTH PROCESS. ' 185
a charge will not follow closely the amount of carbon, since the flame is constantly at work, and ore is added when the melter thinks it advisable rather than when absolutely 'necessary. If the charge is hot, it dissolves the ore rapidly and there is little chance for the flame to do its share of oxidation, while if the charge is cold only a small amount of ore will be added and the oxygen will be derived from the gases. It may be broadly said that if the bath contains 1 per cent, of carbon, 1500 pounds o'f ore may be used in bringing it down to .05 per cent. The first 500 pounds will reduce it to about .80 per cent, of carbon, the second to .40 per cent, and the third will finish the work. If silicon and manganese should be as low during the interval between the first and second ore additions as at a later time, the burning of the carbon might be the same then as later, but either the presence of these protectors or the less favorable physical condition of the slag in a high-carbon bath retards the action at the start. When large quantities of high-silicon or high-manganese pig-iron are used, the first additions of ore are consumed by the unburned excess of these elements, and hundreds and even thousands of pounds of ore may be added after melting before the carbon is affected. Therefore, when it is necessary to charge nothing but pig-iron, it is advisable to have it contain as little silicon as possible, and even then the oxidation of carbon requires several hours. The ore is not lost, for the reduced iron makes up for the metalloids which are burned, so that the weight of the steel may equal or exceed the weight of the pig-iron charged.
The expense of the pig-and-ore process rests in the slow combustion of carbon, for it is impossible to hurry the work without causing' violent boiling of the voluminous slag, producing scorification of ;the hearth and possibly a loss of metal through the doors. The process upon an acid hearth is much slower than on a basic bottom, for 'in the latter case a slag rich in iron does not have disastrous results upon the hearth. Since the fuel consumption per hour is nearly'the same during the period of oreing as it is during the period of melting, there is a considerable decrease in1 product with an increased fuel ratio.
SEC. Xg.—Conditions modifying tlie product.—If the temperature of the metal is high, the last traces of silicon will not be oxidized. In the Bessemer converter the metal may contain as much